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Re: xp requirement document specifies headers

From: Hugo Haas <hugo@w3.org>
Date: Wed, 24 Jan 2001 10:33:37 -0500
To: Mark Nottingham <mnot@akamai.com>
Cc: Henrik Frystyk Nielsen <frystyk@microsoft.com>, "Eric Prud'hommeaux" <eric@w3.org>, xml-dist-app@w3.org
Message-ID: <20010124103337.A7866@tux.w3.org>
On Tue, Jan 23, 2001, Mark Nottingham wrote:
> I also see some reference to footers here, which makes me scratch my
> head a bit. I can see two possible reasons why this would be
> desireable;
> * To "stream" messages, much as chunking and Trailers do in HTTP. My
>   understanding was that XP messages were to be considered and
>   processed only as a whole; processing messages before they are
>   complete leads to complications, both in the transport binding and
>   with XML processing.
> * To imply a processing order by the arrangement of the modules. If
>   so, what significance does placing modules after the body have?

It can be useful to have footers at the generation stage. To take the
example of a checksum again, it is convenient for the XP sender to be
able to include it after the body.

The processing stage is trickier.

> Is the assumption that XP messages will only be considered as a whole
> well-founded? If so, perhaps this should be a requirement or
> restriction of some kind. If not, we should discuss the implications
> (I haven't fully thought them through, I just faintly hear alarm
> bells ;).

I didn't find a requirement about this. R701b[1] expresses the
requirement to define a processing model, but doesn't go into that
much detail.

I remember a discussion about an XP processor starting to process a
message (for example starting to send an XP message back with a
response to an RPC) and then being forced to generate a fault, which
makes me think that indeed XP messages have to be processed as a

On the other hand, R309[2] is about resource constrained device. As
Noah pointed out[3], the issues related to resource constrained
devices have not been discussed in detail; I could imagine a system
with very limited memory wanting to process an XP message "on the

So I think that it is an open issue. But I agree that not considering
XP messages as a whole will lead to complication, and that to keep the
processing model simple, considering XP messages as a whole is a good

  1. http://www.w3.org/2000/xp/Group/xp-reqs-05#z701b
  2. http://lists.w3.org/Archives/Public/xml-dist-app/2001Jan/0021.html
  3. http://lists.w3.org/Archives/Public/xml-dist-app/2001Jan/0020.html

Hugo Haas - W3C/MIT
mailto:hugo@w3.org - http://www.w3.org/People/Hugo/ - tel:+1-617-452-2092
Received on Wednesday, 24 January 2001 10:33:56 UTC

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